Introduction
Pinus massoniana , a member of the pinaceae family, is widely
distributed in the forest area of central and southern China, and
northern Vietnam.1 Due
to its fast-growing, strong adaptability and tolerance to barren
environments, it plays a critical role in forest ecological integrity
restoration and
construction.2,3In addition, it is an important economic tree species commonly used for
timber, wood pulp, rosin and turpentine, which occupies a vital position
in forestry production
industry.2,4Besides, some tissues/organs of P. massoniana including needles,
bark, pollen and turpentine, and extractives extracted from above parts
have been used as traditional Chinese medicines for disease control and
treatment
purpose.5,6Moreover, P. massoniana is also used in landscape and gardening
design, and ornamental
horticulture.7
Calcium (Ca) is an essential nutrient element in plants which occurs in
plant tissue as free Ca2+ or as Ca2+binding to carboxylic, phosphoric and phenolic hydroxyl
groups.8 It has been
reviewed that Ca exhibits diverse functions in various plant biological
processes and cellular
events.9-11 Primarily,
it acts as a structure component of plant cell wall and membrane, which
impacts cell wall rigidity and cell membrane stability and
permeability.9 Thus,
plant growth and development progresses can be directly influenced by Ca
supply.10 Moreover, it
plays an intracellular second messenger role in kinds of plant
physiological and biological processes, such as growth and development,
ion homeostasis, metabolism regulation, signal transduction and a
variety of biotic/abiotic stress
response.9-12 The latest
studies have demonstrated it also participates in programmed cell death,
plant immunity and photosynthesis in
plant.13-15 When
subjecting to a calcium deficient condition, a variety of disorders and
stunned symptoms were observed in horticulture
crops.16 However, after
applying excessive calcium, plants may suffer Ca toxicity and result in
seed germination inhibition and plant growth
reduction.16
It was reported that Ca addition alleviated simulated acid rain induced
seed germination and seedling growth inhibition in P.
massoniana .17 Further
proteomic analysis indicated calcium regulated diverse cellular events
and biological processes in acid rain treated P. massoniana , and
resulted in the tolerance improvement to acid
rain.18 Chen et al.
demonstrated that exogenous hormones and Ca effectively improved the
resistance of P. massoniana to Dendrolimus punctatusattacks.19 Li et al.
studied the impact of various Ca concentrations on the growth and
physiological index of P. massoniana seedlings, and concluded
1.0-2.0 mM soil Ca concentration is the optimal condition for P.
massoniana seedlings
growth.20 Nevertheless,
the knowledge of molecular regulatory mechanisms of Ca on P.
massoniana physiological processes, development and growth is still
relatively limited. Considering the important role of P.
massoniana in both forestry economy and forest ecosystem, it is of
significance to address this issue.
In the present study, the combined physiological and proteomic studies
were performed using P. massoniana seedling cultivated at various
Ca levels to investigate the impact of exogenous Ca on growth and
development, and finally to reveal the underlying molecular mechanisms.
In addition, bioinformatics analysis was implemented to demonstrate the
biological functions and roles of the differential expressed proteins
(DEPs) identified in proteomics experiments, while Ca-related gene
expression was analyzed as well. Our study may facilitate the
elucidation of the potential regulatory role of Ca in P.
massoniana physiology and biology.